Tailoring epilepsy surgery with fast ripples in the intraoperative electrocorticogram

OBJECTIVE: Intra-operative electrocorticography (ECoG) can be used to delineate the resection area in epilepsy surgery. High frequency oscillations (HFOs, 80-500Hz) seem better biomarkers for epileptogenic tissue than spikes. We studied how HFOs and spikes in combined pre- and post-resection ECoG predict surgical outcome in different tailoring approaches. METHODS: We, retrospectively, marked HFOs, divided into fast ripples (FRs, 250-500Hz) and ripples (80-250Hz), and spikes in pre- and post-resection ECoG sampled at 2048 Hz in people with refractory focal epilepsy. We defined four groups of EEG-event occurrence: pre+post- (+/-), pre+post+ (+/+), pre-post+ (-/+) and pre-post- (-/-). We subcategorized three tailoring approaches: hippocampectomy with tailoring for neocortical involvement, lesionectomy of temporal lesions with tailoring for mesiotemporal involvement and lesionectomy with tailoring for surrounding neocortical involvement. We compared the percentage of resected pre-EEG-events, the time to recurrence and the different tailoring approaches to outcome (seizure-free versus recurrence). RESULTS: We included 54 patients (median age 15.5y, 25 months follow-up, 30 seizure-free). The percentage of resected FRs, ripples or spikes in pre-ECoG did not predict outcome. The occurrence of FRs in post-ECoG, given FRs in pre-ECoG (+/-,+/+), predicted outcome (hazard ratio: 3.13 (CI=1.22-6.25); p=0.01). Seven out of eight patients without spikes in pre-ECoG were seizure-free. The highest predictive value for seizure recurrence was the presence of FRs in post-ECoG for all tailoring approaches. INTERPRETATION: FRs which persists before and after resection predict poor post-surgical outcome. These findings hold for different tailoring approaches. FRs can thus be used for tailoring epilepsy surgery with repeated intra-operative ECoG measurements. This article is protected by copyright. All rights reserved